One document matched: draft-ietf-v6ops-ra-guard-02.xml
<?xml version="1.0"?>
<!DOCTYPE rfc SYSTEM "rfc2629.dtd">
<?rfc compact="yes" ?>
<?rfc toc="yes" ?>
<!ENTITY RFC4861 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.4861.xml">
<!ENTITY RFC3971 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.3971.xml">
<rfc category="info" ipr="pre5378Trust200902" docName="<draft-ietf-v6ops-ra-guard-02.txt>">
<front>
<title abbrev="IPv6 RA-Guard">
IPv6 RA-Guard
</title>
<author initials="E" surname="Levy-Abegnoli" fullname="Eric Levy Abegnoli">
<organization>Cisco Systems</organization>
<address>
<postal>
<street>Village d'Entreprises Green Side - 400, Avenue Roumanille</street>
<city>Biot - Sophia Antipolis</city>
<region>PROVENCE-ALPES-COTE D'AZUR</region>
<country>France</country>
<code>06410</code>
</postal>
<phone>+33 49 723 2620</phone>
<email>elevyabe@cisco.com</email>
</address>
</author>
<author initials="G." surname="Van de Velde" fullname="Gunter Van de Velde">
<organization>Cisco Systems</organization>
<address>
<postal>
<street>De Kleetlaan 6a</street>
<city>Diegem</city>
<country>Belgium</country>
<code>1831</code>
</postal>
<phone>+32 2704 5473</phone>
<email>gunter@cisco.com</email>
</address>
</author>
<author initials="C" surname="Popoviciu" fullname="Ciprian Popoviciu">
<organization>Cisco Systems</organization>
<address>
<postal>
<street>7025-6 Kit Creek Road</street>
<city>Research Triangle Park</city>
<region>North Carolina</region>
<country>USA</country>
<code>NC 27709-4987</code>
</postal>
<phone>+1 919 392-3723</phone>
<email>cpopovic@cisco.com</email>
</address>
</author>
<author initials="J" surname="Mohácsi" fullname="János Mohácsi">
<organization>NIIF/Hungarnet</organization>
<address>
<postal>
<street>18-22 Victor Hugo</street>
<city>Budapest</city>
<country>Hungary</country>
<code>H-1132</code>
</postal>
<phone>tbc</phone>
<email>mohacsi@niif.hu</email>
</address>
</author>
<date day="5" month="March" year="2009"></date>
<workgroup>v6ops Working Group</workgroup>
<keyword>I-D</keyword>
<keyword>Internet-Draft</keyword>
<keyword>IPv6</keyword>
<keyword>Router Advertisement</keyword>
<abstract>
<t>
It is particularly easy to experience "rogue" routers on an unsecured
link. Devices acting as a rougue router may send illegitimate RAs. Section 6 of
SeND <xref target="RFC3971" /> provides a full solution to this
problem, by enabling routers certification. This solution does,
however, require all nodes on an L2 network segment to support SeND, as
well as it carries some deployment challenges. End-nodes must be provisioned with
certificate anchors. The solution works better when end-nodes have
access to a Certificate Revocation List server, and to a Network Time
Protocol server, both typically off-link, which brings some bootstrap
issues.
</t>
<t>
When using IPv6 within a single L2 network segment it is possible and
sometimes desirable to enable layer 2 devices to drop rogue RAs before
they reach end-nodes. In order to distinguish valid from rogue RAs,
the L2 devices can use a spectrum of criterias, from a static
scheme that blocks RAs received on un-trusted ports, or from un-trusted
sources, to a more dynamic scheme that uses SeND to challenge RA
sources.
</t>
<t>This document reviews various techniques applicable on the L2
devices to reduce the threat of rogue RAs.
</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t>When operating IPv6 in a shared L2 network segment without complete
SeND support by all devices connected or without the availability
of the infrastructure necessary to support SeND, there is always
the risk of facing operational problems due to rogue Router
Advertisements generated maliciously or unintentionally by
unauthorized or improperly configured routers connecting to the
segment.
</t>
<t>There are several examples of work done on this topic which resulted
in several related studies <xref target="reference1" />
<xref target="reference2" /> <xref target="reference3" />.This document describes a
solution framework for the rogue-RA problem where network segments
are designed around a single or a set of L2-switching devices
capable of identifying invalid RAs and blocking them. The solutions
developed within this framework can span the spectrum from basic
(where the port of the L2 device is statically instructed to forward
or not to forward RAs received from the connected device) to advanced
(where a criteria is used by the L2 device to dynamically validate
or invalidate a received RA, this criteria can even be based on SeND
mechanisms).
</t>
</section>
<section title="Model and Applicability">
<t>RA-Guard applies to an environment where all messages
between IPv6 end-devices traverse the controlled L2 networking
devices. It does not apply to a shared media such as an Ethernet
hub, when devices can communicate directly without going through an
RA-Guard capable L2 networking device.
</t>
<t>Figure 1 illustrates a deployment scenario for RA-Guard.
<vspace blankLines='100' />
<figure><artwork align="left"><![CDATA[
Block Allow
+------+ incoming +---------+ incoming +--------+
|Host | RA | L2 | RA | Router |
| |--------\--------| device |--------/------| |
+------+ \ +----+----+ / +--------+
\ | /
\ |Block /
\ |incoming /
\ |RA /
\_______|_______/
|
|
+---+---+
| Host |
| |
+-------+
]]></artwork></figure>
</t>
<t>RA-Guard does not intend to provide a substitute for SeND based
solutions. It actually intends to provide complementary solutions
in those environments where SeND might not be suitable or fully supported
by all devices involved. It may take time until SeND is ubiquitous in IPv6
networks and some of its large scale deployment aspects are sorted out
such as provisioning hosts with trust anchors. It is also reasonable
to expect that some devices might not consider implementing SeND at
all such as IPv6 enabled sensors. An RA-Guard implementation which SeND-validates RAs
on behalf of hosts would potentially simplify some of these challenges.
</t>
<t>RA-Guard can be seen as a superset of SEND with regard to router
authorization. Its purpose is to filter Router Advertisements based on
a set of criterias, from a simplistic "RA disallowed on a given
interface" to "RA allowed from pre-defined sources" and up to full fladge SeND
"RA allowed from authorized sources only".
</t>
<t>In addition to this granularity on the criteria for filtering out
Router Advertisements, RA-Guard introduces the concept of router
authorization proxy. Instead of each node on the link analyzing
RAs and making an individual decision, a legitimate
node-in-the-middle performs the analysis on behalf of all other
nodes on the link. The analysis itself is not different
from what each node would do: if SeND is enabled, the RA is checked
against X.509 certificates. If any other criteria is in use,
such as known L3 (addresses) or L2 (link-layer address, port number)
legitimate sources of RAs, the node-in-the middle can use this
criteria and filter out any RA that does not comply. If this
node-in-the-middle is a L2 device, it will not change the content of
the validated RA, and avoid any of the nd-proxy pitfalls.
</t>
<t>RA-Guard intends to provide simple solutions to the rogue-RA
problem in contexts where simplicity is required while leveraging
SeND in an context environment consisting of with a mix of SeND capable devices (L2 switches and
routers) and devices that do not consistently use SeND. Furthermore,
RA-Guard is useful to simplify SeND deployments, as only the L2
switch and the routers are required to carry certificates (their
own and the trust anchor certificates).
</t>
</section>
<section title="Stateless RA-Guard">
<t>Stateless RA-Guard examines incoming RAs and decide whether to forward
or block them based solely on information found in the message or in
the L2-device configuration. Typical information available in the
frames received, useful for RA validation is:
<vspace blankLines="1" />
<list style="symbols">
<t>Link-layer address of the sender</t>
<t>Port on which the frame was received</t>
<t>IP source address</t>
<t>Prefix list</t>
</list>
</t>
<t>The following configuration information created on the L2-device
can be made available to RA-Guard, to validate against the
information found in the received RA frame:
<vspace blankLines="1" />
<list style="symbols">
<t>Allowed/Disallowed link-layer address of RA-sender</t>
<t>Allowed/Disallowed ports for receiving RAs</t>
<t>Allowed/Disallowed IP source addresses of RA-sender</t>
<t>Allowed Prefix list and Prefix ranges</t>
<t>Router Priority</t>
</list>
</t>
<t>Once the L2 device has validated the content of the RA frame against the
configuration, it forwards the RA to destination, whether
unicast or multicast. Otherwise, the RA is dropped.
</t>
</section>
<section title="Stateful RA-Guard">
<section title="State Machine">
<t>Stateful RA-Guard learns dynamically about legitimate RA senders,
and store this information for allowing subsequent RAs. A simple
stateful scheme would be for the L2-device to listen to RAs during
a certain period of time, then to allow subsequent RAs only on
those ports on which valid RAs were received during this period. A more
sophisticated stateful scheme is based on SeND, and is described in
<xref target="send-based-ra-guard"/>.
</t>
<t>The state machine for stateful RA-Guard can be global,
per-interface, or per-peer, depending on the scheme used for
authorizing RAs.
</t>
<t>
When RA-Guard is SEND-based, the state machine is
per-peer and defined in [RFC3971].
</t>
<t>When RA-Guard is using a discovery method, the state-machine
of the RA-Guard capability consists of four different states:
<vspace blankLines="1" />
<list style="symbols">
<t>State 1: OFF
<list style="empty">
<t>A device or interface in RA-Guard "OFF" state, operates as if the RA-Guard
capability is not available.
</t>
</list>
</t>
<t>State 2: LEARNING
<list style="empty">
<t>
A device or interface in the RA-Guard "Learning" state is actively acquiring
information about the devices connected to its interfaces. The learning process
takes place over a pre-defined period of time by capturing router advertisements
or it can be event triggered. The information gathered is compared against
pre-defined criteria which qualify the validity of the RAs.
<vspace blankLines="1" />
In this state, the RA-Guard enabled device or interface is either blocking all
RAs until their validity is verified or, alternatively it can temporarily forward
the RAs until the decision is being made.
</t>
</list>
</t>
<t>State 3: BLOCKING
<list style="empty">
<t>A device or interface running RA-Guard and in Blocking state will block ingress
RA-messages.
</t>
</list>
</t>
<t>State 4: FORWARDING
<list style="empty">
<t>A device or interface running RA-Guard and in Forwarding
state will accept ingress RAs and forward them to their destination/
</t>
</list>
</t>
</list>
</t>
<t>The transition between these states can be triggered by manual configuration or
by meeting a pre-defined criteria.
</t>
</section>
<section anchor="send-based-ra-guard" title="SeND-based RA-Guard">
<t>In this scenario, the L2 device is blocking or forwarding RAs based
on SeND considerations. Upon capturing an RA on the interface, the
L2-device will first verify the CGA address and the RSA signature, as
specified in section 5 of [RFC3971]. RA should be dropped in case
of failure of this verification. It will then apply host behavior as
described in section 6.4.6 of [RFC3971]. In particular, the L2
device will attempt to retrieve a valid certificate from its cache
for the public key referred to in the RA. If such certificate is
found, the L2 device will forward the RA to destination. If not, the
L2 device will generate a CPS, sourced with UNSPECIFIED address, to
query the router certificate(s). It will then capture the CPA(s),
and attempt to validate the certificate chain. Failure to validate
the chain will result in dropping the RA. Upon validation success,
the L2 device will forward the RA to destination and and store the
router certificate in its cache.
</t>
<t>In order to operate in this scenario, the L2-device should be
provisioned with a trust anchor certificate, as specified in
section 6 of [RFC3971]. It may also establish a layer-3 connectivity
with a CRL server and/or with and NTP server. Bootstrapping issue in
this case can be resolved by using the configuration method to
specify a trusted port to a first router, and send-based-ra-guard
method on all other ports. The first router can then be used for
NTP and CRL connectivity.
</t>
</section>
</section>
<section title="RA-Guard Use Considerations">
<t>The RA-Guard mechanism is effective only when all messages
between IPv6 devices in the target environment traverse
controlled L2 networking devices. In the case of environments such as
Ethernet hubs, devices can communicate directly without going through
an RA-Guard capable L2 networking device, the RA-Guard
feature cannot protect against rogue-RAs.
</t>
<t>RA-Guard mechanisms do not offer protection in environments
where IPv6 traffic is tunneled.
</t>
</section>
<section title="IANA Considerations">
<t>There are no extra IANA consideration for this document.
</t>
</section>
<section title="Security Considerations">
<t>Once RA-Guard has setup the proper criterias, for example, it identified
that a port is allowed to receive RAs, or it identified legitimiate sources
of RA, or certificate base, then there is no possible instances of
accidently filtered legitimate RA's assuming the RA-Guard filter enforcement
follows strictly the RA-Guard criteria's.
</t>
</section>
<section title="Acknowledgements">
<t>The authors dedicate this document to the memory of Jun-ichiro Hagino (itojun) for
his contributions to the development and deployment of IPv6.
</t>
</section>
</middle>
<!-- =============================================================== -->
<back>
<references title='Normative References'>
&RFC3971;
&RFC4861;
<reference anchor="reference1">
<front>
<title>NDPMon - IPv6 Neighbor Discovery Protocol Monitor (http://ndpmon.sourceforge.net/)</title>
<author initials="" surname="LORIA/INRIA"></author>
<date month="November" year="2007" />
</front>
</reference>
<reference anchor="reference2">
<front>
<title>rafixd - developed at KAME - An active rogue RA nullifier (http://www.kame.net/dev/cvsweb2.cgi/kame/kame/kame/rafixd/)</title>
<author initials="" surname="KAME Project"></author>
<date month="November" year="2007" />
</front>
</reference>
<reference anchor="reference3">
<front>
<title>Discussion of the various solutions (http://ipv6samurais.com/ipv6samurais/demystified/rogue-RA.html)</title>
<author initials="Jun-ichiro" surname="Hagino (itojun)"></author>
<date month="" year="2007" />
</front>
</reference>
</references>
</back>
</rfc>
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